fuzz: BIP 42, BIP 30, CVE-2018-17144

2 files changed, 166 insertions, 0 deletions

diff --git a/src/Makefile.test.include b/src/Makefile.test.include
index 69965ed1b8..461022bbfc 100644
--- a/src/Makefile.test.include
+++ b/src/Makefile.test.include
@@ -344,6 +344,7 @@ test_fuzz_fuzz_SOURCES = \
  test/fuzz/txorphan.cpp \
  test/fuzz/txrequest.cpp \
  test/fuzz/utxo_snapshot.cpp \
+ test/fuzz/utxo_total_supply.cpp \
  test/fuzz/validation_load_mempool.cpp \
  test/fuzz/versionbits.cpp
 endif # ENABLE_FUZZ_BINARY
diff --git a/src/test/fuzz/utxo_total_supply.cpp b/src/test/fuzz/utxo_total_supply.cpp
new file mode 100644
index 0000000000..7813b7854b
--- /dev/null
+++ b/src/test/fuzz/utxo_total_supply.cpp
@@ -0,0 +1,165 @@
+// Copyright (c) 2020 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <chainparams.h>
+#include <consensus/consensus.h>
+#include <consensus/merkle.h>
+#include <kernel/coinstats.h>
+#include <node/miner.h>
+#include <script/interpreter.h>
+#include <streams.h>
+#include <test/fuzz/FuzzedDataProvider.h>
+#include <test/fuzz/fuzz.h>
+#include <test/fuzz/util.h>
+#include <test/util/mining.h>
+#include <test/util/setup_common.h>
+#include <validation.h>
+#include <version.h>
+
+FUZZ_TARGET(utxo_total_supply)
+{
+    /** The testing setup that creates a chainman only (no chainstate) */
+    ChainTestingSetup test_setup{
+        CBaseChainParams::REGTEST,
+        {
+            "-testactivationheight=bip34@2",
+        },
+    };
+    // Create chainstate
+    test_setup.LoadVerifyActivateChainstate();
+    auto& node{test_setup.m_node};
+    auto& chainman{*Assert(test_setup.m_node.chainman)};
+    FuzzedDataProvider fuzzed_data_provider(buffer.data(), buffer.size());
+
+    const auto ActiveHeight = [&]() {
+        LOCK(chainman.GetMutex());
+        return chainman.ActiveHeight();
+    };
+    const auto PrepareNextBlock = [&]() {
+        // Use OP_FALSE to avoid BIP30 check from hitting early
+        auto block = PrepareBlock(node, CScript{} << OP_FALSE);
+        // Replace OP_FALSE with OP_TRUE
+        {
+            CMutableTransaction tx{*block->vtx.back()};
+            tx.vout.at(0).scriptPubKey = CScript{} << OP_TRUE;
+            block->vtx.back() = MakeTransactionRef(tx);
+        }
+        return block;
+    };
+
+    /** The block template this fuzzer is working on */
+    auto current_block = PrepareNextBlock();
+    /** Append-only set of tx outpoints, entries are not removed when spent */
+    std::vector<std::pair<COutPoint, CTxOut>> txos;
+    /** The utxo stats at the chain tip */
+    kernel::CCoinsStats utxo_stats;
+    /** The total amount of coins in the utxo set */
+    CAmount circulation{0};
+
+
+    // Store the tx out in the txo map
+    const auto StoreLastTxo = [&]() {
+        // get last tx
+        const CTransaction& tx = *current_block->vtx.back();
+        // get last out
+        const uint32_t i = tx.vout.size() - 1;
+        // store it
+        txos.emplace_back(COutPoint{tx.GetHash(), i}, tx.vout.at(i));
+        if (current_block->vtx.size() == 1 && tx.vout.at(i).scriptPubKey[0] == OP_RETURN) {
+            // also store coinbase
+            const uint32_t i = tx.vout.size() - 2;
+            txos.emplace_back(COutPoint{tx.GetHash(), i}, tx.vout.at(i));
+        }
+    };
+    const auto AppendRandomTxo = [&](CMutableTransaction& tx) {
+        const auto& txo = txos.at(fuzzed_data_provider.ConsumeIntegralInRange<size_t>(0, txos.size() - 1));
+        tx.vin.emplace_back(txo.first);
+        tx.vout.emplace_back(txo.second.nValue, txo.second.scriptPubKey); // "Forward" coin with no fee
+    };
+    const auto UpdateUtxoStats = [&]() {
+        LOCK(chainman.GetMutex());
+        chainman.ActiveChainstate().ForceFlushStateToDisk();
+        utxo_stats = std::move(
+            *Assert(kernel::ComputeUTXOStats(kernel::CoinStatsHashType::NONE, &chainman.ActiveChainstate().CoinsDB(), chainman.m_blockman, {})));
+        // Check that miner can't print more money than they are allowed to
+        assert(circulation == utxo_stats.total_amount);
+    };
+
+
+    // Update internal state to chain tip
+    StoreLastTxo();
+    UpdateUtxoStats();
+    assert(ActiveHeight() == 0);
+    // Get at which height we duplicate the coinbase
+    // Assuming that the fuzzer will mine relatively short chains (less than 200 blocks), we want the duplicate coinbase to be not too high.
+    // Up to 2000 seems reasonable.
+    int64_t duplicate_coinbase_height = fuzzed_data_provider.ConsumeIntegralInRange(0, 20 * COINBASE_MATURITY);
+    // Always pad with OP_0 at the end to avoid bad-cb-length error
+    const CScript duplicate_coinbase_script = CScript() << duplicate_coinbase_height << OP_0;
+    // Mine the first block with this duplicate
+    current_block = PrepareNextBlock();
+    StoreLastTxo();
+
+    {
+        // Create duplicate (CScript should match exact format as in CreateNewBlock)
+        CMutableTransaction tx{*current_block->vtx.front()};
+        tx.vin.at(0).scriptSig = duplicate_coinbase_script;
+
+        // Mine block and create next block template
+        current_block->vtx.front() = MakeTransactionRef(tx);
+    }
+    current_block->hashMerkleRoot = BlockMerkleRoot(*current_block);
+    assert(!MineBlock(node, current_block).IsNull());
+    circulation += GetBlockSubsidy(ActiveHeight(), Params().GetConsensus());
+
+    assert(ActiveHeight() == 1);
+    UpdateUtxoStats();
+    current_block = PrepareNextBlock();
+    StoreLastTxo();
+
+    LIMITED_WHILE(fuzzed_data_provider.remaining_bytes(), 100'000)
+    {
+        CallOneOf(
+            fuzzed_data_provider,
+            [&] {
+                // Append an input-output pair to the last tx in the current block
+                CMutableTransaction tx{*current_block->vtx.back()};
+                AppendRandomTxo(tx);
+                current_block->vtx.back() = MakeTransactionRef(tx);
+                StoreLastTxo();
+            },
+            [&] {
+                // Append a tx to the list of txs in the current block
+                CMutableTransaction tx{};
+                AppendRandomTxo(tx);
+                current_block->vtx.push_back(MakeTransactionRef(tx));
+                StoreLastTxo();
+            },
+            [&] {
+                // Append the current block to the active chain
+                node::RegenerateCommitments(*current_block, chainman);
+                const bool was_valid = !MineBlock(node, current_block).IsNull();
+
+                const auto prev_utxo_stats = utxo_stats;
+                if (was_valid) {
+                    circulation += GetBlockSubsidy(ActiveHeight(), Params().GetConsensus());
+
+                    if (duplicate_coinbase_height == ActiveHeight()) {
+                        // we mined the duplicate coinbase
+                        assert(current_block->vtx.at(0)->vin.at(0).scriptSig == duplicate_coinbase_script);
+                    }
+                }
+
+                UpdateUtxoStats();
+
+                if (!was_valid) {
+                    // utxo stats must not change
+                    assert(prev_utxo_stats.hashSerialized == utxo_stats.hashSerialized);
+                }
+
+                current_block = PrepareNextBlock();
+                StoreLastTxo();
+            });
+    }
+}